Of all the recent (2006-2011), I'd say 2008.
Agressive riding in all the Grand Tours, possibly besides the Vuelta which was Astana-sandwiched. But the Tour that year was great to watch, drama all along. Ricco & Piepoli testing positive, then Menchov attacking and falling and later on the climb getting a little hungerknock and ofcourse the amazing attack by Sastre, which was really nice to see as a Sastre-fan.
And I don't even have to start about the Giro, the rumours (seen by some as a fact) that Contador just came from the beach. The drama on the mountains, Sella's breakaway adventures, etc.